At present, when underground utilities such as natural gas, potable water, or sanitary sewer pipes are placed in rock, trenches are excavated using large hard rock trenching equipment such as the Vermeer T-655, or possibly even shot using explosives. In these conditions, electric, telephone and cable TV lines are normally strung overhead along poles, mostly due to the difficulty and expense of placing them underground. Thus, in many situations, a solid rock formation will cause utility lines to be located above ground due to the difficulty of underground installation. Many such sites involve mixed conditions involving both a solid rock formation for part of the run and soil for the remainder, often at the beginning and end of the run. In such a situation, rock drilling or trenching equipment may lack the capability to bore through the soil to reach the rock formation.
Directional boring apparatus for making holes through soil are well known. The directional borer generally includes a series of drill rods joined end to end to form a drill string. The drill string is pushed or pulled through the soil by means of a powerful hydraulic device such as a hydraulic cylinder. See Malzahn, U.S. Pat. Nos. 4,945,999 and 5,070,848, and Cherrington, U.S. Pat. No. 4,697,775 (RE 33,793). The drill string may be pushed and rotated at the same time as described in Dunn, U.S. Pat. No. 4,953,633 and Deken, et al., U.S. Pat. No. 5,242,026. A spade, bit or head configured for boring is disposed at the end of the drill string and may include an ejection nozzle for water to assist in boring.
In one variation of the traditional boring system, a series of drill string rods are used in combination with a percussion tool mounted at the end of the series of rods. The rods can supply a steady pushing force to the impact and the interior of the rods can be used to supply the pneumatic borer with compressed air. See McDonald et al. U.S. Pat. No. 4,694,913. This system has, however, found limited application commercially, perhaps because the drill string tends to buckle when used for pushing if the bore hole is substantially wider than the diameter of the drill string.
Accurate directional boring necessarily requires information regarding the orientation and depth of a cutting or boring tool, which almost inevitably requires that a sensor and transmitting device (“sonde”) be attached to the cutting tool to prevent mis-boring and re-boring. One such device is described in U.S. Pat. No. 5,633,589, the disclosure of which is incorporated herein for all purposes. Baker U.S. Pat. No. 4,867,255 illustrates a steerable directional boring tool utilizing a pneumatic impactor.
Directional boring tools with rock drilling capability are described in Runquist U.S. Pat. No. 5,778,991 and in Cox European Patent Applications Nos. EP 857 852 A2 and EP 857 853 A2. However, although directional boring tools for both rock drilling and soil penetration are known, no prior art device has provided these capabilities in a single machine together with the ability to steer the tool in both soil and rock. The present invention addresses this need.
There is also a need in the art for a directional boring tool for rock drilling and soil penetration that provides a percussion hammer driven by liquid fluids, provides indexing of a device for detecting angular rotation (e.g., a sonde) and provides a method for ON/OFF control of the percussion hammer (e.g., pneumatic or liquid driven). In addition, there is a need for an apparatus that provides improved steerability of the drill head.